Fiber optic termination

ABSTRACT

Fiber optic terminations are disclosed for discriminating between potentially damaging energy and energy that has potential utility, internally conditioning and coupling only the energy that may safely be delivered by the optical fiber, particularly where the fiber traverses small radii and tortuous pathways, and harmlessly dissipating the potentially damaging energy within the fiber optic termination.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of priority to U.S. patentapplication Ser. No. 14/617,041, filed 9 Feb. 2015, which isincorporated herein, by reference, in its entirety.

FIELD OF THE INVENTION

This invention relates to fiber optic terminations for coupling tosurgical lasers (e.g., holmium lasers, CTH:YAG and Ho:YAG) and/or otherlow M² beam quality laser sources.

BACKGROUND

Holmium lasers primarily find application in urology for vaporizationand enucleation of hyperplastic prostate tissue (BPH) and breaking apartkidney stones, although additional applications do exist for both softand hard tissue targets. These infrared lasers produce 0.2 joule to 6joule pulses at 350 ms to 750 ms pulse width and 5 pps to 80 pps at 2.08μm to 2.14 μm for average powers ranging from 8 W to 120 W.

Holmium lasers generate multimode laser energy of particularly low M²quality. Thermally induced refractive index gradients and birefringencein holmium laser rods distort the laser output: both beam diameter anddivergence drift during use and myriad modes are generated. Higher powerholmium lasers employ two or more laser heads that are combined toproduce the total laser output, further reducing the beam quality, andsurgical lasers are subjected to jolts and bumps in hospital corridors,freight elevators, thresholds, etc., such that focusing optics are keptas robust and simple as possible. The results of this are focal spotsthat are large, misshapen and unstable, varying widely in parametersfrom manufacturer to manufacturer, throughout a single laser's lifetimeand even within a single surgical session. (Nominal laser focal spotdiameters (defined at 1/e² maximum of semi-Gaussian profiles such thatabout 14% of the laser energy lies outside of the nominal spot diameter)for the first pulses are typically small and circular but balloon intounstable ovals of about 275 μm to about 500 μm.)

Many of the same characteristics of holmium lasers' output that makethem attractive for vaporizing both hard and soft tissues add to thechallenge of safely coupling fiber optics to deliver the energy; thehigh energy infrared pulses vaporize most materials, from polymers tometals. Optical fibers coupled to holmium lasers are routinely damagedby misalignment of the fiber core to the laser and the fibers damage thelaser optics in turn; lenses are pitted or coated with organic andinorganic debris and vapor deposits, reducing performance subtly ordramatically. Subtle damage routinely goes unrecognized untilaccumulations result in catastrophic failure of the laser optics (blastshield, lens, mirrors, rods) or the optical fiber (at the connector oreven meters away, within the patient).

Prior art designs are directed to producing fiber optic terminationsthat are capable of surviving significant core overfill when coupling tothe laser; for example, where overfill energy is spatially filtered andtypically reflected, scattered or absorbed. Some art seeks to capture atleast some of the core overfill energy within the fiber core throughtapered inputs (where the fiber core is larger at the input face) andothers claim to reduce or eliminate coupling to the cladding, to theexclusion of the core.

These prior attempts fail to resolve high attenuation in silica-silicafiber is at 2100 nm which is highly dependent upon the mode populationdistribution within the fiber. Typical silica-silica fiber attenuationranges from 1% to 3% per meter of fiber length for core modes whilecladding modes are attenuated at roughly 10% meter (depending upon thesecondary cladding material). Much of the energy that is lost toattenuation leaks from the fiber, into the polymer cladding and jacket.Fibers fail catastrophically where this leaked energy is of sufficientdensity to melt or burn the polymer layers surrounding the silica-silicafiber: a phenomenon referred to as “burn through” in the laser surgeryfield.

Microbending losses due to defects at the silica core to silica claddinginterface are introduced during fiber preform production. Additionally,defects at the silica cladding to polymer cladding interface, stressesinduced by the EFTE to fiber bonding and dimensional variations in thecore are introduced when the fiber is drawn. Contributing sources totransmission losses may be within the control of the laser fiberdesigner, partially; for example, by selecting the best base fibermaterial to work with, establishing strict dimensional limits for coreand claddings, and selecting among available polymer claddings.Unfortunately, insufficient cladding thickness continues to be asignificant source of attenuation in holmium laser fibers.

Furthermore, cladding modes suffer greater attenuation than low ordercore modes and predispose a laser fiber to burn through failure. Instriving to produce fiber terminations that survive spatial overfill ofthe fiber core, most current holmium laser fiber designs introduce newsources of cladding mode excitation. FIG. 1 illustrates two causes ofcladding mode excitation in holmium laser fibers resulting from fibertermination defects. FIG. 1A depicts a fiber 5 where the fiber axis 10is misaligned with the laser focus axis 15 such that the fiberacceptance cone α is misaligned with the laser focus cone θ and FIG. 1Bdepicts an angle polished fiber face 30 where the fiber face plane 35 isnot orthogonal to the laser focus axis 40 such that the acceptance coneα of the fiber 45 is misaligned with the focus cone θ.

Cladding mode excitation that is due to the laser performance or damagedoptics can only been mitigated by a fiber termination design, i.e. beamblooming (FIG. 2). Beam blooming is generally the result of thermalgradients within the laser, but some prior art fiber terminationsamplify this problem by reflecting a portion of the laser energy backinto the laser cavity, further destabilizing it or even pitting the rodface. FIG. 2A depicts a nominal holmium laser focus where the lens 50 isselected to focus a nominal output 75 of the laser rod at the focalplane 55 such that the focal spot diameter 60 is smaller than the core65 of the fiber 70 and the focal cone angle θ is lower than the minimumacceptance cone α of the fiber 70. When holmium laser rods heatunevenly, the refractive index of the rod changes non-uniformly,producing a variable, and typically larger, diameter beam. FIG. 2Bdepicts the laser focus of FIG. 2A where the output 80 of the laser rodhas bloomed in diameter due to thermal lensing such that it fills moreof the focusing lens 85 causing the focal cone angle θ to increase,overfilling the fiber acceptance cone α and causing the focal spotdiameter 90 to increase, overfilling the core 95 of the fiber.

Where the laser output blooms, the fiber meridional mode NA may beoverfilled, as in FIG. 2B, but because the fiber core is larger than thenominal laser focal spot diameter, the core is not spatially overfilled.The overfilling of the fiber acceptance angle goes unnoticed in mostcases because the polymer coating over the fiber's glass cladding isable to weakly guide the angular overfill, but should such fibers besubjected to bending stress, e.g. by the surgeon wrapping the fiberabout his hand to gain a good grip, or by the fiber bending at thecystoscope working channel port, or just distal to the laser connection,higher order modes will be converted to cladding modes that are poorlyguided, degrading the polymer cladding in a cascade of failure thattypically ends catastrophically.

FIG. 3 illustrates mode conversion (mode promotion) within anexaggerated angle, tapered input fiber (neglecting refraction at theair:glass interface for simplicity in this illustration) where higherorder focal modes 120 below the maximum acceptance cone angle of thefiber (12.7°) are reflected within the taper 105 at the core:claddinginterface at 130 and are raised in angle of propagation by the taperhalf angle of 2.5° to 12.5°. When the promoted rays encounter the taperwall a second time 135 they are again promoted by 2.5° at thecore:cladding interface. The resulting angle of 15° exceeds thesilica-silica numerical aperture such that, on a subsequent encounterwith the taper wall 140, the rays pass through the core:claddinginterface. These rays are again reflected, but by the glass:airinterface of the polymer cladding free taper, and are promoted to 17.5°and finally to 20° just prior to entering the cylindrical fiber 110. Inthat the un-tapered fiber is coated with a low refractive index polymer,these 20° modes will be guided as cladding modes until they are lost toattenuation, exit the distal tip of the fiber, or contribute to a burnthrough failure.

FIG. 4 illustrates a method of compensating for mode conversion ofhigher angle excited modes where the same angle higher order mode asdepicted in FIG. 3 150 is refracted at 160 by a negative curvature lens155 such that the refracted mode never encounters the taper wall 175,but instead reflects for the first time within the cylindrical fiber 170at 165. Using such a concave lens input, tapered input fibers mayperform as well as, or better than, many straight input fibers, yetthese types of terminations can excite and convert cladding modes undermore stressful conditions such as beam blooming or scatter in damagedoptics.

Other fiber termination strategies, e.g. FIG. 5, may also inadvertentlylaunch cladding modes. U.S. Pat. No. 7,090,411 (Brown) discloses a glassferrule 235 surrounding a polymer denuded fiber 230 with unpolished (sawcut) glass faces 220 & 245 acting as diffusers as well as internalmultifaceted reflectors and reduced diameter input fibers. Suchscattering elements, as exemplified by 220 and 245, scatter laser focalrays 210 with the bulk of the overfill energy being redirected towardpolymer clad 250 and ETFE buffered 265 segments of the distal fiber suchthat very high order scattered modes may couple to the fibercore:cladding within the polymer-free segment proximal to 215 and becomeguided as cladding modes within the polymer clad fiber at 250. Employingtapered fibers in the reverse of FIG. 3 will convert higher order modesto lower orders only when the taper axial alignment is assured and taperangles are lower than the highest order modes excited within the fibercore.

Accordingly, improvements in fiber termination technologies aredesirable.

SUMMARY

A first embodiment is a fiber termination that includes a portion of anoptical fiber disposed within and fused to a ferrule. In thisembodiment, the optical fiber can have a terminus, adjacent to theterminus a clad fiber and distal from the terminus and adjacent to theclad fiber a polymeric-coated fiber. The clad fiber includes a silicacore and an F-doped silica cladding; the polymeric-coated fiber includesthe clad fiber carrying one or more polymeric coatings. The ferrulecarries at least one furrow, where the furrow or furrows cover all 360radial positions about the ferrule. Notably, the clad fiber and theferrule are fused at a clad fiber and ferrule terminus forming aterminal face. Additionally, in this embodiment, the silica core and theferrule having refractive indices that are approximately equal.

Another embodiment is a fiber termination that includes a portion of anoptical fiber disposed within and fused to a ferrule, the terminationhaving on the terminal face a concave lens. In this embodiment, theoptical fiber includes a terminus, adjacent to the terminus a clad fiberand distal from the terminus and adjacent to the clad fiber apolymeric-coated fiber. Notably, the polymeric-coated fiber is the cladfiber carrying one or more polymeric coatings. Herein, the clad fiber isdisposed or partially disposed within the bore of the ferrule and anouter edge of the clad fiber is fused to a bore wall of the ferrule at acommon terminus of the clad fiber and the ferrule. In this embodiment,the common terminus carries a concave lens which is centrosymmetric to alongitudinal axis of the clad fiber. Herein, the concave lens has adiameter which is about 45% to about 125% of a diameter of the cladfiber core at the common terminus.

Yet another embodiment is a fiber termination that includes an opticalfiber having a terminus, adjacent to the terminus a clad fiber anddistal from the terminus and adjacent to the clad fiber apolymeric-coated fiber. The clad fiber disposed within the bore of aferrule, where an outer edge of the clad fiber is fused to a bore wallof the ferrule at a common terminus of the clad fiber and the ferrule.The ferrule carrying at least one furrow, the furrow or furrows coveringall 360 radial positions about the ferrule. The common terminus carryinga concave lens which is centrosymmetric to a longitudinal axis of theclad fiber, the concave lens having a diameter which is about 45% toabout 125% of a diameter of the clad fiber core at the common terminus.

Still another embodiment is a fiber termination that includes an opticalfiber having a terminus, adjacent to the terminus a clad fiber anddistal from the terminus and adjacent to the clad fiber apolymeric-coated fiber. The clad fiber disposed within the bore of aferrule, where an outer edge of the clad fiber is fused to a bore wallof the ferrule at a common terminus of the clad fiber and the ferrule.The common terminus carrying a compound lens that includes a concavelens radially centered relative to the clad fiber, and a convex annularlens that has a diameter that is less than a diameter of the ferrule.

BRIEF DESCRIPTION OF THE FIGURES

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingfigures wherein:

FIG. 1A and FIG. 1B illustrate two causes of cladding mode excitation inthe holmium laser fibers resulting from fiber termination defects foundin prior art;

FIG. 2A and FIG. 2B illustrate holmium laser beam bloom and itsconsequences;

FIG. 3 is a cross-section of a tapered input fiber, showing the fate ofa high order laser focus mode in coupling to a fiber through the taperedsegment of U.S. Pat. No. 6,282,349;

FIG. 4 is the same taper input as depicted in FIG. 3, showing thealtered fate a high order laser mode when coupled through an input faceequipped with a concave lens according to U.S. Pat. No. 7,488,116;

FIG. 5 is based upon U.S. Pat. No. 7,090,411, showing quartz ferrulesleeved optical fiber termination with integral beam scatteringelements;

FIG. 6 depicts the one embodiment of the herein presented optical fibertermination;

FIG. 7 is one example of a ferrule useful in the optical fibertermination in FIG. 6;

FIG. 8 is an example of a ferrule in an optical fiber terminationshowing a single, helical slot, groove or furrow with an acute angleleading edge cut into the outer diameter of the protective ferrule abouta tapered input fiber;

FIG. 9 is a representation of the fates of various launch modes within atapered input fiber fused within a helical groove equipped ferrule,shown for example in FIG. 8;

FIG. 10A and FIG. 10B are isometric views of a fiber within a closelyfitting ferrule for fusion;

FIG. 11 is a schematic of the production of one example of the hereindescribed optical fiber termination;

FIG. 12A is another example of the herein described optical fibertermination; FIG. 12B is an expanded cross-section of FIG. 12A taken online B-B; FIG. 12C and FIG. 12 D are expanded views of detail C anddetail D of the termination shown in FIG. 12B; FIG. 12E is an expandedview of detail E shown in FIG. 12D;

FIG. 13 is a representation of the fates of various launch modes withina straight fiber termination equipped with a helical coil mode strippingand centering element as shown in FIG. 12; and

FIG. 14A is another example of the herein described optical fibertermination; FIG. 14B is a cross-section of FIG. 14A taken on line A-A;FIG. 14C is an expanded view of the detail in FIG. 14B.

FIG. 15 in yet another example of an optical fiber termination, thisexample depicting the interaction of rays through a laser focus lens toan annular lens and then into a taper fiber core.

FIG. 16 is a depiction of the optical fiber termination in FIG. 15,therein showing the fusion of the tapered fiber core to the ferrule atthe terminus, and a compound lens that includes an outer convex lens, anannular convex lens, and a radially centered concave lens.

While specific embodiments are illustrated in the figures, with theunderstanding that the disclosure is intended to be illustrative, theseembodiments are not intended to limit the invention described andillustrated herein.

DETAILED DESCRIPTION

Disclosed herein is a fiber optic termination which affects a moreuniform and diffuse absorption of spatial overfill energy and segregatesoverfill energy and potentially damaging modes from efficient excitationof modes which are safe to deliver to the bulk fiber. The disclosedfiber optic termination includes a tapered or straight clad fibercarrying a mode stripper (e.g., a thin wall silica tube that includesenergy-redirecting furrows, cuts, channels, or slots; a silica spring;or a ferrule that includes energy-redirecting furrows, cuts, channels,or slots).

As used herein, parts or portions of devices or items may be describedas quartz or silica parts. Generally, these terms are interchangeableand any embodiment reciting a quartz part should be understood toinclude or disclose a silica part. As used herein, “cladding modes”refer to light that is not guided by a glass-core-to-glass-claddingboundary but is guided by the glass-to-polymer-cladding boundary,regardless of the source. Multimode fibers that are used in holmiumlaser surgery are step index and “doubly clad” with a fluoropolymercoating of lower refractive index than the fluorine-doped (F-doped)silica cladding. A secondary numerical aperture (NA) of approximately0.33 to 0.41 is produced by this polymer coating, such that it is oftenreferred to as “secondary cladding”. These fibers are buffered (or“jacketed”) with a relatively thick layer of polymer, typically ethylenetetrafluoroethylene (ETFE) copolymer (refractive index ˜1.4 @ 633 nm)that is dyed blue or green to enhance visibility within the surgicalfield. Additionally and as used herein, a “polymeric-coated fiber”refers to a clad fiber carrying a fluoropolymer cladding and/or afluoropolymer jacketing and/or another polymeric coating.

In one embodiment, a fiber termination includes an optical fiber havinga terminus, adjacent to the terminus a clad fiber and distal from theterminus and adjacent to the clad fiber a polymeric-coated fiber.Herein, a “clad fiber” refers to a fiber that includes a silica core andan F-doped silica cladding. The polymeric-coated fiber includes the cladfiber carrying one or more polymeric coatings. The fiber terminationadditionally includes a mode stripper fused to the clad fiber; the modestripper includes at least one silica spring and/or silica tube. Thesilica tube has or carries at least one furrow, the furrow or furrowscovering all 360 radial positions about the silica tube. Preferably, thesilica spring and/or silica tube and the clad fiber have refractiveindices that are approximately equal.

In one example, the mode stripper includes a silica tube having ahelical furrow. Preferably, the helical furrow has a leading edgeselected from the group consisting of an edge perpendicular to a fiberlongitudinal axis, an edge angled relative to the fiber longitudinalaxis, and a mixture thereof. In one instance, the mode stripper includesa silica tube which has a helical furrow, the helical furrow having aleading edge which transitions from an edge perpendicular to a fiberlongitudinal axis to an edge angled relative to the fiber longitudinalaxis. In another instance, the leading edge of the helical furrow isangled at about 38° relative to the fiber longitudinal axis.

In another example, the mode stripper is a silica spring. Preferably,the silica spring is fused to the clad fiber such that the clad fiber isexposed within the spring pitch. Herein, the spring pitch is understoodto mean the distance from center to center in adjacent coils of thespring. As used in relation to the silica spring fused to the cladfiber, portions of the surface of the clad fiber are not covered by theglass of the silica spring when the spring and fiber are fused together.

As described herein, the fiber termination requires at least one modestripper. While a plurality of diameter-equal mode strippers, fused tothe clad fiber, is possible a plurality is not necessary to the functionof the invention.

In another example, the fiber termination includes a silica ferrulefused over the mode stripper. Preferably, the silica ferrule is fused tothe clad fiber proximal to the terminus. In one instance the silicaferrule can be fused to the mode stripper, where, preferably, the silicaferrule is not fused to the mode stripper. In a preferable example, thesilica ferrule is a fused-quartz ferrule; that is, the silica ferrule iscomposed of fused quartz.

The silica ferrule, preferably, has or carries at least one furrow, thefurrow or furrows covering all 360 radial positions about the silicaferrule. In one instance, the silica ferrule has a helical furrow. Thatis, the furrow transitions about the ferrule in a helical pattern alongthe longitudinal length of the ferrule (e.g., see FIG. 8). The furrowcan have a leading edge selected from the group consisting of an edgeperpendicular to a fiber longitudinal axis, an edge angled relative tothe fiber longitudinal axis, and a mixture thereof. Preferably, thesilica ferrule includes a furrow that has an edge angled relative to thefiber longitudinal axis. In another instance, the silica ferrule isfused over a mode stripper; where the mode stripper can be a silica tubethat has a helical furrow. Here, the mode stripper helical furrow,preferably, has a leading edge that transitions from an edgeperpendicular to a fiber longitudinal axis to an edge angled relative tothe fiber longitudinal axis.

In yet another example, the fiber termination has a terminus whichincludes a convex or conical lens on the silica ferrule. Preferably, theterminus includes a concave lens that covers at least 90% of the silicacore. Even more preferably, the terminus includes both a concave lens onthe silica core and a convex or conical lens on the silica ferrule.Still more preferably, the concave lens is formed, at least in part,from the silica core (i.e., from a concave shaping of the silica coreterminus).

In still another example, the fiber termination includes a tapered cladfiber. That is, at least a portion of the clad fiber, between theterminus and the polymeric-coated fiber, is tapered. In one instance,the mode stripped can be fused to the tapered clad fiber, preferably,with a silica ferrule fused to the clad fiber proximal to the terminus.Notably, in this instance, the silica ferrule is not fused to the modestripper, and preferably, there is an internal vacancy between the modestripper and the silica ferrule.

The fiber termination can further include connectors adapted to join thefiber termination to a laser source, and/or parts adapted to hold theoptical fiber to the fiber termination, or hold the parts of the fibertermination together during use or, for example, sterilization. In thisinstance, the fiber termination can, for example, include a crimpferrule bound to the polymeric-coated fiber and surrounding the modestripper and/or a silica ferrule; and/or include a connector ferrulesurrounding the mode stripper and/or silica ferrule.

Another embodiment is a method of manufacturing an optical fibertermination. One method includes providing an optical fiber thatincludes a denuded portion adjacent to a terminus (e.g., by denuding aportion of an optical fiber). Then forming a mode stripper on thedenuded optical fiber by either (A) positioning a silica tube about alength of the denuded optical fiber; fusing the silica tube to thedenuded optical fiber; and then forming furrows in the silica tube; or(B) positioning a silica spring about a length of the denuded opticalfiber; and then fusing the silica spring to the denuded optical fiber.The process can further include positioning the mode stripper within asilica ferrule; and then sealing the silica ferrule to the opticalfiber. Preferably, the mode stripper is fused to the clad fiber, thenthe silica ferrule is positioned about the fiber and mode stripper, andthen the silica ferrule is fused to the clad fiber. The process canfurther include forming furrows in the silica ferrule. Preferably, theprocess further includes forming a concave lens on the terminus of thedenuded optical fiber.

Still another embodiment is a method of manufacturing an optical fibertermination that includes fusing a silica tube to a terminus of a cladfiber; and forming one or more furrows in an exterior surface of thesilica tube. Preferably, this process additionally includes providing amode stripper having one or more furrows between the clad fiber and aninterior surface of the silica tube; wherein the mode stripper is fusedto the clad fiber.

Additional embodiments and features can be understood in relation to thefigures: for example, FIG. 6 depicts a fiber optic termination thatincludes a means for addressing fusion and transmissive problems of theprior art; this fiber optic termination scatters spatial and angularoverfill energy throughout a larger section of the fiber connector forstraight and/or tapered fibers. The embodiment of the fiber optictermination depicted in FIG. 6. includes a tapered fiber 270 within atapered bore 280 of a quartz tube 275 where the angle of the taperedbore 280 closely matches the angle, diameter or outer surface of thetapered fiber 270. The depicted embodiment further includes perforations285 periodically placed along the length and circumference of the tube275, where the perforations 285 can, for example, vent gases capturedbetween the tapered fiber 270 and the tapered bore 280 of the tube 275that would otherwise interfere with fusion of the fiber to the tube.Laser focal rays exceeding the acceptance cone angle for meridionalmodes within the fiber, regardless of where the rays entered the fusedface 310, are refracted or reflected upon encountering the periodicperforations 285. While the perforations depicted in FIG. 6 aresymmetrically spaced for ease of illustration, random, helical,close-packed, or other arrangement of the perforations 285 are possible;asymmetric perforations can prevent high order modes from passingthrough the quartz tube 275 without encountering a perforation 285.

FIG. 7 illustrates another example of a quartz tube 320. In thisinstance, the tube 320 can include a cylindrical bore 330 (e.g., forfusion to a straight fiber), with circumferential slots 370, shownangled and elongated. The circumferential slots 370 can coveralternating and overlapping segments of the 360° tube circumference fromthe outer diameter 340 to the inner diameter provided by the cylindricalbore 330. The width of the slots can be wider at the tube OD 350 than atthe tube ID 360. The differentiating width of the slots 370 can beprovided by varying the focal cone of a laser used to form the slots andfor ease of differentiating between the slot openings. The slots can bepitched forward; that is, oriented with the narrow opening 360 moreproximal to a termination or face than the wide opening 350. Thispitched arrangement can produce reflective surfaces (as defined bySnell's Law for rays entering the tube from the right (the fiber opticalaperture after a fiber has been fused within the tube 320)).

FIG. 8 depicts a single, helical slot within the wall of the tube. Inanother instance the tube can include a plurality of helical slots thatare the same or different. The helical slot can be pitched forward, asdescribed above, and/or have a differentiating width, as describedabove. In one instance, the compound angle of the front face of thehelical slot can be shaped (have an angle relative to an incoming lightray) to cause total internal reflection of spatial overfill rays as wellas leaking cladding mode rays.

The slots, perforations, cuts, or grooves in the tube can be positioned,pitched, and sized to address the following issues:

a) meridional and skew modes may be differentially affected by the slot,furrow or groove geometry and a plurality of pitch and path may beemployed;

b) spatial overfill and stripped cladding modes may be affected byvirtue of the helical pitch alone and a helical slot, furrow or groovewith less forward pitch to no forward pitch (i.e., perpendicular to thelength of the tube) may be employed;

c) refracted rays entering the fused fiber assembly without scatteringmay be redirected by a helical slot, furrow or groove with a leadingedge face that is parallel to the laser focal plane;

d) total internal reflection (TIR) or redirection of unwanted modes orradiation can be provided by including angled, intermittent angled,angled helical, and/or angled intermittent helical slots, furrows orgrooves (“redirecting grooves”) that do not penetrate the tube to thebore (or to the fiber cladding);

e) overfill radiation and cladding modes can be redirected at differentpositions along the length of the tube by, for example, includinggrooves, slots, or furrows of varying depth of penetration;

f) skew rays can be redirected into elements surrounding the tube by,for example, including redirecting grooves with differentiating (e.g.,opposite) pitches, where, for example, the pitches overlap, where atleast one of the slots does not completely penetrate to the tube bore,and/or where the groves may be included on different sections of thetube;

g) cladding modes and higher order modes prone to promotion to claddingmodes can be stripped by, for example, fusing (e.g., total fusion of thefiber and the tube) the fiber and the tube by way of a continuous pathwithin closely matching refractive index material (i.e. between thefiber and the tube);

h) a curved input surface, or lens, that extends radially from thecenter of a fiber core but does not cover the entire core (and/or laserfocal spot diameter at the fused input face) can separate modepopulations within the laser focus for differential treatment within thefiber termination, and

i) a gradient index (GRIN) lens may be employed for discriminating amongmodes within the laser focus for differential fates within the fibertermination.

FIG. 9 depicts, in cross section, the propagation and/or stripping oflight rays (375, 380, 385, 390) within, for example, the a fiber optictermination that includes the tube depicted in FIG. 8. Herein, each rayrepresents of a category of laser focus energy imparting the input face420 of the termination. Two rays 375 and 380 that enter the terminationthrough the quartz tube 400, where ray 375 represents angles outside ofthe fiber's maximum acceptance angle (e.g., ˜12.7° for meridional modes,higher for skew modes) and ray 380 represents angles at or below thefiber's maximum acceptance angle but within the tube 400. Two rays 385and 390 enter the fiber core 405, where ray 385 represents rays at aboutthe fiber's maximum acceptance angle and those that are above thefiber's maximum acceptance angle, ray 390 represents rays at anglessufficiently below the base fiber maximum acceptance angle such thatmode promoting reflections from the taper wall do not convert the raysto cladding modes.

In one method of using the herein described fiber optic termination, ray375 is diffracted at the planar termination face 420 and passes throughthe fiber as the angle of incidence on the fiber surface is too high;then the ray encounters a leading edge 415 of a helical groove (bottom)where the ray is reflected into the connector ferrule 425. Ray 380 canbe guided at an interface 410 between the tube 400 and the core 405. Theinterface can be between the tube and cladding and/or between thecladding and the core. Ray 380 reflects at the interface and thenencounters a leading edge 415 of the helical groove 395 where the ray isreflected into the connector ferrule 425. Ray 385 enters the terminationat the core face but is of an angle very near the maximum acceptanceangle of the silica core. After being guided through one reflection atthe interface 410 within the taper, the ray enters the tube 400 andencounters a leading edge 415 of the helical groove 395. This ray 385 isthen reflected into and absorbed by the connector ferrule 425. Ray 390represents rays that enter the fiber core at the input face 420 and areof low enough angles to be captured by the tapered fiber/fibercore/silica core.

The herein described embodiments prevent rays 375 and 385 from beingcaptured by silica core 405 and delivering those rays as cladding modesto a polymer clad portion of the fiber, as would occur if the core was“air clad”, that is not fused to the tube 400. In one example, a concavesurface at the input 420 to the silica core 405 may refract some rayssuch as ray 385 to angles that can be captured by the silica core 405and conducted to the distal fiber. This example may further include apartial fusion of the core 405 to the tube 400.

While the example depicted in FIG. 9 discriminates between spatialoverfill and angular overfill in the termination, this discriminationmay be limited by the instability of the laser focus and errors inalignment of the termination to the nominal laser focus. With a flatinput face 420, the boundary between the energy permitted to excitemodes within the fiber core 405 and rejected and redirected is within adynamic continuum of the presented energies. A perfect termination wouldinclude centricity of the fiber to the laser focus, alignment of thefiber to the focal axis, a round and invariable diameter laser focus,and a planar fiber input face that is parallel to the laser focal planeand produce a demarcation between unwanted and desirable energy whichwould be consistent temporally and about the circumference of thetermination. Unfortunately, the temporal instability and asymmetry ofthe laser beam quality and the sum of the tolerances in any terminationdesign (e.g., as depicted in FIG. 9) cannot divide the energy continuumconsistently in either space or time. That is, elements of eachpopulation will be mixed with elements of the other with respect totheir fate.

Total fusion of a relatively thin fiber, straight or tapered, within arelatively thick wall tube is extremely difficult to accomplish withoutdefects (total fusion being circumferential fusion of a substantiallength of the proximal fiber, i.e. 1 cm to 2 cm, within the tube).Contrary to rationales offered in the prior art, the competing demandsof centricity and displacement of gases between the fiber cladding andthe tube bore lead to defect formation during fusing, even in terminalfractions of less than 1 mm.

When heating a thick wall tube, relatively large areas of the tube reachsintering temperature at approximately the same time, even with thepositional precision of a CO₂ laser in applying heat for fusion. Closelyfitting fibers (within a tube bore) tend to fuse preferentially whereclose contact is closest: where the tube bore wall is tangent to thefiber cladding outer diameter. As illustrated in FIG. 10A, the contactbetween the fiber 455 and the tube 465 is the line of tangency 470between the closely matching fiber outer diameter 450 and the tube borediameter 460; fusion will occur at this line of contact first, and overa considerable length of the fiber in the tube. The difference betweenthe fiber 450 diameter (0.44 mm) and the tube bore 460 (0.460 mm) isdepicted in FIG. 10A is about 20 μm because to depict the ˜2 μmdifference of a close fit, one assuring centricity, simply cannot beclearly represented in a drawing, but the principles illustrated remainvalid for an ˜2 μm difference.

In and of itself, preferential fusion of part of the diameter of a fiberwithin a closely fitting tube is not a problem, but a consequence ofthis fusion is the formation of a very thin film of air on either sideof the fusion line, expanding to ˜2 μm on the opposite side of thefiber. As fusion proceeds FIG. 10B, areas of very thin film air (orgases produced by combustion of organic contaminants on the fiber outerdiameter or the tube bore) tend to be trapped as islands absent fusion475, often evident by interference patterns.

This problem is solved by increasing the difference between the fiberdiameter and the tube bore to roughly 40 μm to 80 μm and by restrictingmovement of the fiber within the bore during fusion. While the appliedCO₂ laser energy for melting the tube is still dispersed over arelatively large area, the area where the tube bore begins to close dueto surface tension within the melt is quite small: a ring of fusion thatis about 100 μm forms between the fiber and the tube when heated underrotation in a focused CO₂ laser beam. By scanning the laser distallyalong the tube (with the fiber centered within), from the plane wherefusion initiates, the fusion front advances uniformly and a large gap ismaintained between the fiber outer diameter and the tube bore wall toallow expanding atmosphere and gases of combustion to escape.

Prior art methods for centering and restricting a fiber from moving offcenter during fusion have proven inadequate to the task due to (a)remaining variability in centricity and (b) separation of the centeringmechanism to the fusion region permitting static attraction and meltsurface tension to overcome fiber rigidity. As a result, the centricityof the fiber within the tube is generally far from perfect and the coreand cladding may be visibly distorted within the fusion region; greaterdistortion generally results where tube wall thicknesses exceed thefiber diameter and eccentricity errors appear larger where the gapbetween the tube bore and the fiber diameter is small.

Embodiments of the invention disclosed herein offer solutions to theseissues while enabling far greater discrimination among desirable andundesirable portions of the laser focus energy.

Another embodiment includes a thin walled quartz tube or silica springfused about the clad fiber and a thicker walled ferrule fused about thethin walled quartz tube or spring. This embodiment reduces or preventsthe formation of any centricity error or defects in the fusionjunction(s). FIG. 11 depicts steps in the manufacture of thisembodiment, for a straight termination fiber. The manufacturing processcan begin with a stripped optical fiber; in FIG. 11A, the optical fibercan include, for example, a 200 μm core within a 240 μm clad fiber 480(wherein the distances are to the outside diameter of the fiber). Theclad fiber 480 is exposed when the Tefzel buffer 485 and the polymerhard cladding 490 have been removed, for example over about a 1.5 cmsection.

As used herein, an optical fiber is understood to include a plurality ofparts. Within the fiber is a core or fiber core that typically consistsof a synthetic silica glass. The core carries a synthetic silicacladding that typically consists of a fluorinated silica glass—thecombination of the core and the cladding is referred to as a clad fiber.Commonly, the clad fiber further carries one or more polymeric coatings,for example a polymer hard cladding (often carried by the silicacladding) and a Tefzel buffer layer (often carried by the polymer hardcladding). The process of removing the polymeric coatings can be calledstripping or denuding the optical fiber; in some circumstances the cladfiber is called a denuded fiber.

FIG. 11B depicts the addition of a thin wall quartz tube 495 to the cladfiber 480, e.g., with a bore of roughly 280 μm and an outer diameter of420 μm. Notably, the thicknesses provided herein indicate one example ofthe invention but are primarily provided for tolerances and relativethicknesses. The thin walled quartz tube 495 can be fused over the fibersegment 480 producing a sleeved fiber (or over-clad fiber) section onthe proximal terminus. FIG. 11C depicts the result from the productionof a helical furrow 500 over, e.g. about 50%, 60%, or 70% of, theproximal terminus of the thin walled quartz tube 495. The helical furrow500 can include a leading edge angled at approximately 38° relative tothe fiber longitudinal axis (TIR profile). Preferably, in thisembodiment, the helical furrow does not contact or reach to the proximalterminus but stops short of either or both ends of the quartz tube 495.A heavy wall quartz ferrule 510 can then be positioned over the thinwalled quartz tube 495 and fused to the thin walled quartz tube 495. Forexample, FIG. 11D depicts a heavy wall quartz ferrule 510 with a bore525 of roughly 500 μm and an outer diameter of about 1.63 mm fused overthe furrows 500 of the thin walled quartz tube 495. Preferably, thefusion ceases just after the sleeved fiber furrow 500 ends. Morepreferably, the fusion yields a hermetically sealed, helical space 535about the fiber segment 480. In one example, a second helical furrow 515can be added to the heavy walled quartz ferrule 510; preferably, thisfurrow includes a leading edge 520 at an angle appropriate for totallyreflecting any laser radiation that imparts that edge. Thus atermination is produced presenting a fused face consisting of a core andcladding protected by a surrounding quartz ferrule upon which acurvature (lens) 540 may or may not be machined.

In certain embodiments, the addition of the thin walled quartz tube wasfound to be necessary for the production of the furrows close to or incontact with the clad fiber. While, one of ordinary skill in light ofthe disclosure herein could envision furrows or grooves positionedwithin the clad fiber, the cladding thickness is physically too thin toaccept grooves of any significant depth without optically affecting thefiber core or the evanescent field within the cladding. Notably, theapplication of the thin wall quartz tube described above provides thematerial necessary to applying the furrows without adverse effect to theoptical performance of the fiber within.

FIG. 12A depicts a completed fiber termination including the metallicend 625 of the termination. FIG. 12B shows a cross-sectional view of thecomponents of the completed fiber termination. This termination caninclude an optical fiber 555 leading to a non-tapered clad fiber 550 (asection that was denuded of coating and buffer polymers). The clad fiber550 can carry a thin walled quartz tube 565, preferably, equipped with afurrow that transitions 585 from a centro-symmetric profile 580 (wherehigh order modes such as cladding modes refract substantially along thesleeve axis or reflect across the fiber axis) in a termination-proximalportion of the sleeved fiber, to a TIR profile 595 (with the acute,reflecting angle leading edge 590, where high order modes reflectsubstantially orthogonal to the fiber axis and into the connector wall)in a termination-distal portion. The completed fiber termination canfurther include a thick walled ferrule 570 fused to the quartz tube 565at the terminus 575. The termination can further include an adhesiveseal 560 between the optical fiber 555 and the ferrule 570; and/or ametallic crimp 625 which seats a gasket 615 to the ferrule 570 at theseal 560 and seals the internal vacancies 620 of the furrowed, sleevedfiber for example protecting the vacancies from intrusion of water vaporduring sterilization.

In one example, the quartz tube 565 is fused within the surrounding,thick walled ferrule 570 but only adjacent 575 to the input terminus asopposed to over the entirety of the furrowed sleeve. In another example,the input face 630 of the termination is equipped with a negative(concave) lens 600 on approximately 90% of the fiber core, transitioningto a slightly convex annulus 605 about the outer 10% of the fiber coreand the F-doped silica cladding 610. The compound curvature of the inputface 630, as opposed to the flat input face of the example in FIG. 9,separates higher order focal rays at the periphery of the laser focusfrom lower order rays at the center of the focus, refracting andexciting lower order modes within the fiber core while refracting higherorder modes in the opposite direction, to angles that may be strippedfrom the surrounding ferrule 570 by a furrow or furrows applied to theouter diameter (not shown in FIG. 12).

The compound curvature of the lenses 600 and 605, the placement of thetransition in curvatures and the nature of the transition (gentle tosharp) serve to compensate for vagaries in discrimination betweendesirable and undesirable energy populations within the unstable laseroutput and for errors in centricity and angular alignment within thetermination. In using only a fraction of the fiber core for acceptingdesirable radiation, the boundary between acceptable and unacceptableradiation may be maintained within the core dimension such thatunacceptable energy that may inadvertently drift into the transitionregion within the core diameter continues to be refracted to angles thatare subject to redirection within the furrow features of the sleeveand/or the outer ferrule rather than coupling to the core.

Variants possessing transitioning furrow profiles (or multiple profilesupon various sections of the sleeved fiber and/or the surroundingferrule) enable selection of the location(s) within the connector's(metal) ferrule where unwanted energy is to be dumped.

Preferably, non-tapered (or straight input) fibers (e.g., FIG. 12) andtapered input fibers (e.g., FIG. 14) include a negative lens 600 on theinput face. In one instance, tapered input fibers include a negative(concave) lens with a larger radius of curvature and thereby avoid modepromotion of higher order modes by reflections on the conical taperwall. Preferably, the curvatures of the lens on a straight input and thelens on a tapered input fiber will differ due to differences in theeffective fiber NA at the fusion face. The diameter of the concave lens(or the placement of the transition from concave to convex) willdetermine the highest order mode accepted for coupling to the fiber andthe lowest order mode that is excluded from coupling to the fiber. Thecurvature of the convex annulus will determine how far off axial thatthose excluded modes are refracted.

FIG. 13 depicts the result of laser rays imparted upon a fibertermination (e.g., as shown in FIG. 12). Notably, the laser focus rays(705, 720) can be separated by the fiber termination and the higherorder rays 695 are dispersed into the ferrule 660. The separation of therays can be based upon what portion of the fused input face 675 theyimpart upon. In this example, a clad fiber 655 with a silica core 650fiber carries a helical coil 710 of quartz fused onto the F-doped silicacladding 655. Herein, a helical coil 710 is employed as opposed to theabove described thin walled quartz tube with furrows. The helical coilonce fused to the silica cladding 655 yields a helical furrow 715 thatreaches or penetrates to the surface of the clad fiber. The fibertermination can further include a quartz ferrule 660 (e.g., 18 mm long)having a bore diameter 690 that is slightly larger than the outerdiameter of the helical coil 710 fused upon the fiber. Preferably, theferrule has an outer diameter of roughly 1 mm to 1.8 mm.

In this example, the ferrule 660 is fused to the clad fiber 655 at theinput face 675. This fusion can be accomplished by heating the quartzferrule near the opening that will become the input face 675, forexample by way of a CO₂ laser, causing the bore of the ferrule to shrinkuntil it fuses to the clad fiber at 665.

FIG. 13 additionally depicts an input face 675 that includes a concavelens 685 across a majority of the silica core 650, and a convex lens 680upon, preferably, the balance of the input face 675. In another example,a portion of the input face not covered by the concave lens can becovered by an annular prism/annular lens/conical lens presenting a sharptransition from the annular profile to the concave. The input face canbe shaped by adjusting a CO₂ laser focal point for vaporization of thequartz ferrule, fused region, and/or the clad fiber. Notably, an “airgap” 670 remains (preferably, a partial vacuum where the quartz ferruleis sealed to the fiber at the distal opening, as shown in FIG. 12) aboutthe fiber cladding near the input face 675 and within the furrows 715.

In one instance, low angle holmium laser focal energies 705 and 720within the central ˜85% of the beam profile (approximately the nominalfocal spot diameter as defined by 1/e² energy maximum) address thecentral and concave surface 685 of the fused input face 675 and arerefracted, exciting substantially axial modes 725 and 730 within thefiber core 650. Were these low order modes to diverge enough to contactthe core:cladding (650:655) boundary of the fiber, they will be easilyguided.

For the purposes of this example, the high angle holmium laser focal 695within the peripheral ˜15% of the semi-Gaussian beam profile (outside ofthe nominal 1/e² focal spot diameter), is assumed to be within theacceptance cone of the base fiber NA. That is, if the fiber corediameter larger and the fiber input face flat, aligned with and centeredupon the laser focal spot, rays 695 would excite core modes that wouldbe guided within the fiber, albeit as high order modes that are moresusceptible to promotion to modes that are damaging to the fiber withindeflected portions of the fiber. The higher order rays 695 of theholmium laser focus impart the convex portion of the fused input face675 and are refracted in the opposite manner as the lower order rays 705and 720. The resulting modes are not guided by the core:cladding(650:655) boundary of the fiber, but leak into coils of the silicaspring 710 and are reflected at substantially orthogonal angles 700 tothe fiber axis and are absorbed by the surrounding SMA ferrule wall.Notable, throughout the disclosure reference is made in SMA componentsor parts as SMA connections are common for the connection of opticalfibers to laser sources. Other connections/connectors are available,including but not limited to FC, ST, SMB, SMC, GT5, MCX, MMCX, BNC, FME,TNC, and N-type connectors.

Accordingly, the compound curvature of the termination input face 675separates laser focal population into rays of two distinct populations:a high order (represented by rays 695 that are redirected 700 andabsorbed) and a lower order population (represented by rays 705 and 720that are guided 725 and 730); thereby disrupting what would have been acontinuum of modes provided by a flat input face termination. The twonew mode populations are further separated by redirection in the modestripping segment (the helical coil of silica 710 fused to the fibercladding 655) where, in terminations lacking this feature, these rayswould be guided as cladding modes and would predisposed the fiber toburn through failure in deflection. A second redirecting groove orfurrow such as that depicted in FIG. 8 may be produced upon the ferrule660 outer diameter to augment redirection of unguided modes within thetermination in that not all of the laser focal energy will behave aspredictably as those depicted in FIG. 13 within an actual termination.

In contrast to prior art where laser focus that spatially overfills afiber core is scattered at one or more random scattering elements withinthe termination, the invention described herein is capable of activelyselecting and redirecting both spatial and angular overfill energies, aswell as other energy that may be undesirable to couple to the fiber. Thedisclosed structure eliminates the random redirection and the couplingof undesirable energy modes within the fiber by division of thecontinuum of mode populations (within the laser focal cone) intopopulations that are readily guided or readily redirected. Theabsorption distributions are also controlled and diffuse within thedisclosed terminations, whereas prior art absorptions are largelyconcentrated at loci that are particularly susceptible to thermaldamage.

The herein disclosed terminations also serve to provide centering ofboth tapered and straight fibers within the larger bore of thesurrounding ferrules, thereby providing minimally distorted andconcentric fusion junctions (as discussed above with reference to “totalfusion”). The mode stripping elements that are fused about the claddingsof the fibers may be positioned a few millimeters distal to the fusionjunction to produce a localized larger diameter upon which a closelyfitting surrounding quartz ferrule bore may be disposed. The close fitprovides an excellent, proximate and refractory centering element for arelatively large gap between the clad fiber within the ferrule bore thatis unavailable in prior art. Prior art solutions that centered the fiberproximate the fusion junction, such as U.S. Pat. No. 7,309,167 and U.S.Pat. No. 7,699,535, employ a chamfer to locally increase the ferrulebore diameter at the fusion junction while using the original, closefitting ferrule bore for local centering. These prior art examples havethe unintended consequence of refracting and scattering any overfillenergy, at the conical bore surface, to high angles within thesurrounding ferrule. This unintended and uncontrolled scatter is carriedby the air clad ferrule to the back of the termination where heat labilematerials reside and optical coupling to the polymer clad fiber mayoccur. The herein described terminations provide fiber to ferrulefusions with improved angular alignment and centricity withoutscattering; lessening of the thermal dissipation load within thetermination; and reduction of cladding modes coupled to the fiber in thedistal portion of the termination.

The embodiments provided herein disperse “rejected” overfill energy overan area greater than provided in the prior art. For example, in U.S.Pat. No. 6,282,349 overfill energy is absorbed by a brass crimp ferruledelivered by way of a transmissive quartz ferrule while fixing andcentering the fiber within the termination through crimping about theETFE buffer. This dual function of the crimp limits the maximum spatialoverfill of approximately 2.5 W, above which the ETFE buffer melts andfailure ensues. Herein, the rejected energy is dispersed over a farlarger area, where that area, and the area where thermally labilematerials reside, is bisected by a SMA nut attachment point throughwhich heat is communicated to the external heat sink (or “expansionnut”; FIG. 14, reference no. 800). Accordingly, the fiber terminationcan use softer and/or more labile materials for affixing the fiberwithin the termination and for reducing the stresses imparted upon thefiber at proximal connector fixation point. For example, adhesives andseals made of the following can be employed herein: graphite, Vespel,silicones, UV cure adhesives, and/or cyanoacrylates.

Turning to FIG. 14, the fiber optic termination can include, in additionto the optical fiber and the ferrule, a plurality of mechanical partsdirected toward holding the termination and connecting the terminationto a laser source. In one example, FIG. 14A depicts the externalsurfaces of a complete fiber optic termination; therein the terminationcan include a bend limiting boot 860 connected to a heat-dissipatingexpansion nut 805, with a protruding input face 820. FIG. 14B shows theinternal components of a cross-section of FIG. 14A. Therein, thetermination can include a SMA nut 800 that is pressed into the expansionnut 805 and the bend limiting boot 860. FIG. 14C depicts further detailsof the termination.

In this embodiment, the device, preferably, includes a modediscriminating input face 820, for example including a compound concaveand convex curvature (e.g., shown in FIGS. 12 and 13). The input face820 is carried on the terminus of a tapered fiber 865 and a quartzferrule 880. In the depicted example, the clad fiber is a tapered fiber865 carrying a silica coil 870 which is fused to the clad fiber surface.The clad fiber 865 and silica coil 870 are within a quartz ferrule 880.Preferably, the quartz ferrule 880 includes a TIR groove 875 or helix.The TIR groove 875 redirects undesirable energy in the quartz ferrule880 to the SMA ferrule 810. Notably, redirected undesirable energy isabsorbed by and heats the SMA ferrule 810, which resides within thelaser port affixed to the larger laser cabinetry. The quartz ferrule 880seats 825 onto a gasket 830 (e.g. a silicone gasket) within a crimpferrule 835. The crimp ferrule 835 is crimped 840 onto the buffer layers845 on the optical fiber. The crimp preferably provides a vacuum tightseal by compression of the gasket 830 between the crimp ferrule 835 andthe quartz ferrule seat 825 as well as by physically pressing into theoptical fiber buffer layers 845. The vacuum seal is further improved bya first tube 850 heat-shrunk about the crimp ferrule 835, and a secondtube 855 heat-shrunk about a portion of the SMA ferrule 810 that holdsthe crimp ferrule 835. Furthermore, the SMA ferrule 810 is positionedwithin the SMA nut 800. The ferrule 810 and nut 800 are separated by agap 815 which closes or disappears when the SMA is engaged within thelaser port.

Preferably, the energy absorbing portions of the termination (e.g., theSMA ferrule 810) are separated from the thermally labile portions (e.g.,the buffer layers 845 and the gasket 830) of the termination by aconduit for conducting the heat outside of the assembly. In FIG. 14C,the conduit for conducting the heat is from the input face 820, throughthe TIR groves 875 into the SMA ferrule 810. The heated SMA ferrule 810,preferably, conducts heat to the SMA nut 800 and not to the crimpferrule 835.

The maximum laser power available to launch into small core fibers forsurgery is typically in excess of the needs of the surgical procedureand/or the safe carrying capacity of the fiber (particularly whenconsiderable deflection is required to reach the surgical target). Thesurgical need is, in part, a function of the perceived risk/reward ofsurgical safety versus surgical efficacy. Notably, one expects that theadditional power, or power in higher repetition rates (favoring new“stone dusting” techniques), would be useful if such power can bedelivered safely and reproducibly to a surgical target.

Commercially available small core fibers “waste-off” as much as 15% ofthe applied laser power within the termination and it is often the heatdissipation capacity (maximum 2.5 W) of the termination that effectivelylimits the maximum power rating, not the carrying capacity of the bulkfiber. Conversely, small core fibers carrying average powers that arewell under the manufacturers' maximum power recommendations commonlyfail within the deflected ureteroscope working channel due topredisposition to burn through failure though carrying large populationsof higher order modes and/or cladding modes. (Burn through failureswithin deflections that are 50% larger than the smallest deflectioncapacity of flexible ureteroscopes are common with as little as 0.2joules per pulse at 5 Hz.)

Prior art cannot address the selective coupling of only those laserfocal spot modes that are (a) most effective in achieving the surgicalgoal and are (b) most compatible with passage of tortuous paths inreaching the surgical target. Although larger core fibers are nottypically tasked with negotiating tight turns in advancing to thesurgical target, these fibers do inadvertently suffer tight turns, notsolely at the laser connector (for which most manufacturers supply somestrain relief or bend limiter for mitigation of the risk) but at thesealing cap at the cystoscope working channel entrance and where thesurgeon attempts to retain purchase upon the fiber for control, wherebend limiters cannot be placed. Some surgical fibers come equipped withtorque control devices (e.g., pin vises) that attach to a fiber by wayof localized compression of the ETFE, e.g. side fire fibers for BPH, butsuch devices have not won acceptance in laser lithotripsy because thecompression of the fiber by the pin vise often leads to burn throughfailure at or in close proximity to the torque controller.

As shown in FIG. 13, the sharp demarcation between convex 680 andconcave 685 portions of the input face 675 serves to differentiallyrefract the peripheral rays (e.g., 695) relative to more centrallylocated rays (e.g., 705 and 720). In some instances, the amount ofredirected energy, refracted to imping on the inner bore of the SMAferrule (See e.g., FIG. 14, 810), may exceed a thermal absorptioncapacity of the SMA connector. (e.g., causing deformation or melting ofthermally labile materials) This can be particularly problematic whenthe redirected energy rays are of substantially similar focal angle andlocation relative to the fiber's longitudinal axis and thereby terminateat a substantially similar longitudinal local within the SMA ferrule.Preferably, these peripheral rays 695 or a portion thereof areredirected to delocalized locations.

Turning to FIG. 15, the input face can include an annular lens 905,separating the concave lens 900 from the convex lens 910. Notably, FIG.15 is not to scale and the diameter of the ferrule 930 is, preferably,about 2 to about 10, or about 4 to about 6 times the diameter of the(tapered) fiber 925 core at its maximum (e.g., at the terminus). Thetapered fiber 925 is fused 920 within the cylindrical bore 940 of thesurrounding, spiral grooved 945 quartz or silica ferrule 930. In thisillustration, the laser focus lens 915 produces a spot diameter that issignificantly larger than the tapered fiber 925 core at its maximum(occurring at the concave input face 900). The annular lens 905 refractsspatial/angular overfill rays (e.g., the top four and bottom four raysas shown in FIG. 15) such that they impart the residual bore 935 justbehind the fusion region 920. As such, the ferrule 930 becomes anannular waveguide clad with air for the overfill rays.

In some instances (e.g., larger core fibers and/or non-tapered fiberterminations), the structure depicted in FIG. 15 can be sufficient forreducing the high order mode excitations within the fiber, obviating theneed for an on-fiber mode stripper as shown in FIGS. 11 and 13. Inanother instance, annular lens 905 can be extended from the concave lens900 to the outside edge of the ferrule 930. Preferably, the terminationis free of a sharp transition between the annular lens 905 and theconcave lens 900.

It is important to note that, in smoothing the demarcations of theconcave lenses on the fiber terminations, for any size of fiber, taperedor not tapered, the critical dimension of the concave lens diametershould not be greatly affected; for best control of the collimation ofthe laser focus within the fiber, the concave lens diameter should be(a) equal to or smaller than the fiber core diameter for fiber coresequal to or smaller than the laser focal spot diameter or (b) equal toor smaller than the laser focal spot diameter for fibers with corediameters larger than the focal spot diameter. Alternatively, thediameters of the lenses (on the input face) to the diameter of the cladfiber can be provided as a ratio. Herein, for example, the diameter ofthe concave lens can be about 40% to about 150% the core diameter of theclad fiber, that is the diameter of the clad fiber core at the terminusor where fused to the ferrule. Preferably, the diameter of the concavelens is about 45% to about 125%, about 45% to about 60%, about 65% toabout 90%, about 85% to about 125%, or about 95% to about 110% of thediameter of the clad fiber core. Furthermore, the lenses on the inputface are preferably centrosymmetric with the clad fiber; that is, lensesare radially centered relative to the clad fiber core.

The pattern of redirection of overfill energy by the spiral groove(i.e., the amount and longitudinal location where the overfill energy isdumped into the surrounding metallic fiber connector ferrule) isvariable and affected by the depth of the groove, the angle of thegroove leading edge, and the pitch of the spiral of the groove. In thecase of standard SMA fiber connectors, for example, roughly ½ of the SMAferrule 810 is located within the laser chassis and in intimate contactwith the laser SMA port such that it may be advantageous to provide agroove or grooves where the grooves are closely spaced at the front ofthe termination and loosely spaced at the rear of the termination.Alternatively or in addition, it may be advantageous to provide a grooveor grooves where the angle of the leading edge of the groove reflectsrays in substantially orthogonal or forward angles within the portion ofthe SMA ferrule that is within the laser chassis, transitioning to moreacute angles as the ferrule emerges from the chassis constrained portionof the SMA. Where alternative SMA ferrule 810, expansion nut 805 and/orSMA nut 800 designs are provided, as have recently become commerciallyavailable, or some alternative, a concentration of the excess energyabsorption within the rear of the termination may be beneficial.

For reference, the relative dimensions of the fiber terminationsdescribed herein are approximated in FIGS. 12 and 14 where the metalliccrimp and/or energy absorbing ferrule (625 in FIGS. 12 and 835 in FIG.14) major diameter is typically 2.5 mm and the quartz ferrule (570 inFIGS. 12 and 875 in FIG. 14) is typically 1.63 mm.

Further detail can be found in FIG. 16 which is a greatly enlargedcross-sectional view of approximately the first 2 millimeters of the endof a fiber termination. Therein, a tapered optical fiber, having anF-doped silica clad (1000) silica core 1010, is fused (at a fusion 1030)to the interior surface of a quartz ferrule 1020. Behind the fusion 1030of the tapered optical fiber 1010 to the ferrule 1020 is an “aircladding” or air gap 1070 between an exterior surface of the F-dopedsilica cladding 1000 and the interior surface of the ferrule 1020.Notably, this air cladding or air gap can include air or any gas or gasmixture (e.g., nitrogen, argon, helium, and mixtures thereof).Preferably, the diameter 1045 of the radially centered concave lens 1040is less than the maximum diameter 1015 of the fiber's silica core 1010,that is, the diameter of the silica core at the fusion 1030. In thisdepiction, the annular convex lens 1050 surrounding theradially-centered concave lens 1040 includes a diameter 1055 that isabout twice that of the concave lens 1040 and has a radius of curvaturethat is approximately one half that of the concave lens. Still further,FIG. 16 includes an outer convex surface 1060 diameter 1025 which isequal to the diameter of the quartz ferrule. Notably and as describedabove the diameter 1055 of the annular lens can be expressed as apercentage or ratio to the diameter of the ferrule. In examples, thediameter of the annular lens 1050 is about 10%, about 20%, about 30%,about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about100%, or 100% of the diameter of the ferrule. In some embodiments of thefiber termination described herein, the annular lens outer diameter isless than twice the concave lens diameter. In other embodiments, theannular lens has an outer diameter that is substantially the same as thediameter of the ferrule. In instances where the diameter of the annularlens is 100% (the same as) of the diameter of the ferrule, thetermination does not include an outer convex surface 1060.

The present invention has been described with reference to the preferredembodiments provided above; those skilled in the art will recognize thatchanges may be made in the form and detail without departing from thespirit and scope of the invention.

What is claimed:
 1. A fiber termination comprising: an optical fiberhaving a terminus, adjacent to the terminus a clad fiber and distal fromthe terminus and adjacent to the clad fiber a polymeric-coated fiber,the clad fiber including a silica core and an F-doped silica cladding,the polymeric-coated fiber including the clad fiber carrying one or morepolymeric coatings; and the clad fiber disposed within the bore of aferrule the ferrule carrying at least one furrow, the furrow or furrowscovering all 360 radial positions about the ferrule; the clad fiber andthe ferrule fused at a clad fiber and ferrule terminus forming aterminal face; the silica core and the ferrule having refractive indicesthat are approximately equal; wherein the clad fiber has a diameter, theferrule has an outside diameter and the ratio of the ferrule outsidediameter to the clad fiber diameter is about 2 to about
 10. 2. The fibertermination of claim 1, wherein the furrow is a helical furrow; thehelical furrow having a leading edge selected from the group consistingof an edge perpendicular to a furrow longitudinal axis, an edge angledrelative to the furrow longitudinal axis, and a mixture thereof; whereinthe leading edge has a pitch relative to the fiber longitudinal axis. 3.The fiber termination of claim 2, wherein the helical furrow has aleading edge that transitions from an edge perpendicular to the furrowlongitudinal axis to an edge angled relative to the furrow longitudinalaxis.
 4. The fiber termination of claim 2, wherein at least a portion ofthe leading edge of the helical furrow is angled at about 38° relativeto the furrow longitudinal axis.
 5. The fiber termination of claim 2,wherein the pitch of the leading edge is constant.
 6. The fibertermination of claim 2, wherein the pitch of the leading edge varies. 7.The fiber termination of claim 1, wherein a depth of the furrow isconstant.
 8. The fiber termination of claim 1, wherein a depth of thefurrow varies along a ferrule longitudinal axis.
 9. The fibertermination of claim 1, wherein the clad fiber is tapered adjacent tothe terminus.
 10. The fiber termination of claim 9 further comprising anair cladding between the clad fiber and the ferrule.
 11. The fibertermination of claim 1, wherein the terminal face carries a lens. 12.The fiber termination of claim 11, wherein the lens is a compound lensthat includes a concave lens, the concave lens radially centeredrelative to the clad fiber; the concave lens having a diameter that isless than a diameter of the ferrule.
 13. The fiber termination of claim12, wherein the concave lens is bounded by a convex annular lens. 14.The fiber termination of claim 13, wherein the annular lens has an outerdiameter, and wherein the annular lens outer diameter is less than twicethe concave lens diameter.
 15. The fiber termination of claim 13,wherein the annular lens has an outer diameter, and wherein the annularlens outer diameter is substantially the same as the diameter of theferrule.
 16. A fiber termination comprising: an optical fiber having aterminus, adjacent to the terminus a clad fiber and distal from theterminus and adjacent to the clad fiber a polymeric-coated fiber; theclad fiber disposed within the bore of a ferrule, where an outer edge ofthe clad fiber is fused to a bore wall of the ferrule at a commonterminus of the clad fiber and the ferrule; the ferrule carrying atleast one furrow, the furrow or furrows covering all 360 radialpositions about the ferrule; the common terminus carrying a concave lenswhich is centrosymmetric to a longitudinal axis of the clad fiber, theconcave lens having a diameter which is about 45% to about 125% of afiber core diameter at the common terminus.
 17. The fiber termination ofclaim 16, wherein the furrow is a helical furrow; the helical furrowhaving a leading edge selected from the group consisting of an edgeperpendicular to a fiber longitudinal axis, an edge angled relative tothe fiber longitudinal axis, and a mixture thereof.
 18. The fibertermination of claim 17, wherein the helical furrow has a leading edgethat transitions from an edge perpendicular to a fiber longitudinal axisto an edge angled relative to the fiber longitudinal axis.
 19. A fibertermination comprising: an optical fiber having a terminus, adjacent tothe terminus a clad fiber and distal from the terminus and adjacent tothe clad fiber a polymeric-coated fiber; the clad fiber disposed withinthe bore of a ferrule, where an outer edge of the clad fiber is fused toa bore wall of the ferrule at a common terminus of the clad fiber andthe ferrule; the common terminus carrying a compound lens that includesa concave lens radially centered relative to the clad fiber, and aconvex annular lens that has a diameter that is less than a diameter ofthe ferrule.
 20. The fiber termination of claim 19, wherein the ferrulecarries at least one furrow, the furrow or furrows covering all 360radial positions about the ferrule.